Plastic material



ing to from'3O to 60 pounds steam pressure.

7 25 time to time.' The use of hardrubber or =56 rcha, or may be combined with a com Patented Aug; ,9, 1922. I I

UNITED STATES PATENT OFFICE.

nacnrn a. xnmr, or nnsr onmen, NEW :rnasnr, nssreuoa 'ro wnsrnnn nnnc'rnrc comranv, INCORPORATED, or raw YORK, N. 'Y., a coaroaa'non or new YORK.

rmsrrc MATERIAL.

N Drawing. Application filed July 12, 1984. 361181 1T0. 785,681.

This invention relates to plastic matepounding material such for example as a rials, and its object is to produce a thermo- 'wax or gum to modify its mechanical charplastic .material which is particularly suitacteristics to suit some particular condition. able for .the insulationof electrical con- In the preferred process, the raw rubber is ductors. compounded with 12% of sulphur byweight',

It is a common practice toinsulate electhese materialsbeing thoroughly mixed totrical conductors by means of a rubber com gether b 'Working on the rolls of a standpound, which, when vulcanized provides a soft elasticcovering which is also agood 1o insulator. This compound, as a rule, containsfrom 2% to 5% sulphur by weight and is vulcanized at a temperature correspondard' rub er mill. After being thoroughly mixed,}the compound is then vulcanized or heat treated by maintaining it at a tempera-. ture of approximately 225 C. for a period ofapproxlmately one hour. For general purposes, the best result is obtained if the above percentage of sulphur is employed, but this proportion may be'changed somewhat tomeet particular conditions, and the resulting material will have the same general characteristics. Thus, when using 8%, :sulphur, the resulting material resembles smoked sheet rubber, the hardness and toughness being little changed by reducing the temperature to 0 C. and. when 16%.

Such an insulated conductor, while satisl5 factory for many uses, has not proven satisfactory for long submarine cables, since the soft rubber absorbs Water and the resulting osmotic swelling may cause 7 deleter ous changes in the electrical constants, of the 20 cable. For this reason, gutta percha is almost universally used for. insulating submarine cable conductors; but, because of its high cost and limitedsource of supply, various substitutes have been proposed from brittle atthis temperature. The temperature for the heat treatment prefe"abl is mainsemi-hard rubber as the insulating matetained at approximately 225 but for rial for submarine cables offers important commercial use should notbe less than 200 advantages because of its low conductance,j+-GZ and it should not exceed 280 C, The low dielectric constant and its, limited absorption of water, and in a copending application of Robert R. Williams, Serial No. 703,660, filed April 2; 1924, there is disclosed a method of applying such aninsulation to a conductor without the disadvantages resulting when such a material is vulcanized on the conductor itself. What' is commerc ally lmown as hard rubber conv tains'from 20 to 30% sulphur, while the ma terial' designated as semi-hard rubber con- 40 tains from 16 to 120% sulphur. These materials, however, are thermoplastic only to a limited degree, and their application to an electrical conductor necessitates special precautions. p I In accordance with a feature of the present invention, rubber and sulphur are compounded in the proper proportions and given a heat treatment whereby the resulting material possesses characteristics similar Q to gutta percha as regards its thermoplastic thermoplastlcltyof this material 18 largely property and can be extruded and similarly due to disaggregation of the highly aggremanipulated without special precautions.- gated polyprene or rubber sulphide mole-' This material may be used alone as an insucules through the agency of suitable heat,

' lating material to taxe the place of gutta but a period of approximately one hour is The insulating material obtained by fol lowing this process is-very similar to gutta percha in its physical properties and can be extruded andworked in much the-same manner. In its electrical characteristics, it is asgood or better than gutta,percha, and it can be obtained at a considerable saving in cost. For certain uses itmay be found desirable to mix this material with a comounding material-such at balata, parafline, Bitumen, etc.- A material 'es eciallysuite able for the insulation of su marine 'con- .ductors is obtained by mixing this material with approximately 25% its weight of .balata.' 3

' It is believed thatl the-high degree of,

similar results are obtaine even though which theory is borne out b 'thefact that sulphur is used, the resulting product becomes minimum time required for. this treatment depends upon the temperature maintained.

sufli'cient inthe case of a temperature of there is a halt in the vulcanization of heating process. Thus, a compound containing the right proportions of rubber and sulphur may be vulcanized at ordinary vulcanizing li 'temperatures corresponding to 50 to 60 pounds steam pressure, and then may later be subjected to a temperature'of 200 to 280 'C., and the resulting product will have the same mechanical characteristics as it would have had ifv the heating treatment had been completed in one step. Instead of employing a high temperature for'disaggregating the rubber sulphide molecules, it is possible thatsimilar results might be obtained by the use of a suitable catalytic agent.

Because of the fact that the heat treatment does not have to be performed continuously, it is possible to obtain a material having satisfactory thermoplastic properties 7 by. mixing reclaiming rubber stock with theproper amount of sulphur, and then heating to a temperature of approximately 225 C. and maintaining the material at this "temperature for a period of approximately one hour.

Although the material made in'accordance with this process is especially suitable for use in insulating electrical conductors, its physical propertles are such that it may be used in difi'erent fields as a substitute for gutta percha and one that can be obtained at a much lower cost.

The term thermoplastic, as used in this specification and the appended claims,

3 should be taken to denote the property, possessed by a materiahof varying its plasticity in accordance with variations in its tempera ture. By qualifying the term thermoplastic in this specification and the appended 40 claims by comparing such property with the thermoplastic properties of gutta percha it is intended that the term, as qualified, should 1 approximately represent such variations in plasticity as are manifested by gutta percha within the temperatures, which on one hand exist at the sea bottom or other places where conductors insulated with gutta percha are ordinarily placed for operation and ma be below zero degrees centi'grade, and w 1Cl1 on the other hand are ordinarily maintained during the extruding process in the manufacture of gutta percha insulated cables and do not exceed 100 C.

- What is claimed is:

1. A material having the thermoplastic roperties of gutta percha comprising ruber mixed with 8 to 16% sulphur an subjected to a temperature sufficiently high to render the material thus thermoplastic.

properties of 'tta perchajcomprising rubber mixed wit 8 to 16% sulphur, and subjected to a temperature of not-less than 200 C. andnot more than 280 C.

a 3. A material having the thermoplastic 2. A material having the thermoplastic properties of gutta percha comprising rub ber mixed with 8 to 16% sulphur, and subjected to a temperature of approximately 225 C. for a period of approximately one hour. c I

4. A material having. the thermoplastic properties of gutta percha comprising rubber mixed with 12% sulphur by weight, and

subjected to a temperature of approximately 225 C. fora period of approximately one hour. a 1

5. A material comprising rubber mixed with 8 to 16% sulphur and heat treated, so that. it is nonplastic at a temperatureof 10C. and can be extruded at a temperature of 80C. Y c

6. A material having the thermoplastic properties of gutta percha comprisin -rubber mixed with 8 to 16% sulphur an heat treated at a temperature of approximately 225 0., to which is added an insulating material. I

7. A thermoplastic material comprising a rubber-sulphur compound heat treated at a temperature of approximately 225 (3., to

which is added ba ata.

8. The process of producing a material having the thermoplastic properties of gutta to 20 C. the properties of gutta percha which enable it to serve effectively as an insulator for submarine cables.

which is non-plastic at a temperature of 10 C. and can be extruded at a temperature of 80 C. which comprises compounding rubber with from 8% to 16% of sulphur and heat ing to a temperature of from 200 to 280 C.

11.'The process of producing a material having the thermoplastic properties of gutta percha, which comprises compounding rubher with 12% sulphur and subjecting the al comprising principally rub 10. The process of producing a material compound to a temperature of 225 C. for a period of approximately one hour. I

12. The process of producing a material having the thermoplastic properties of gutta percha, which comprisescompounding rubber with from8 to 16% sulphur and subjecting such compound to a heat treatment sufli? cient to vulcanize the material, and then subjecting the material to a temperature of 200 to 280 C. to disaggregate the highly aggregated rubber sulphide molecules.

13. The process of producing a materialhaving the thermoplastic properties of gutta percha, whichconsists in cpmpounding rubher with 12% sulphur, maintaining the comclaiming rubber stock a suflicient amount of pound at a temperature of approximately sulphur to bring the total sulphur content W 225 C. for a period of ap roximately one" up to from 8 to 16%, and heating said mixhour, and mixin the resu ting compound ture for a period of approximately one hour 6 with approximate 25% balata. at a temperature offfrom 200 to 280 C.

l4. The process of producing a material In witness whereof, I hereunto subscribe having the thermoplastic properties of gutta my name this 9th day of July, A. D. 1924( percha, which consists in mixing with re- ARCHIE R. KEMP. 

